INVESTIGATIONS OVER USING MIRRORS AND PRISMS IN GEODETIC MONITORING OF BUILDING STRUCTURES

The paper describes research works over displacement monitoring system based
on distance measurements, which could allow the determination of movements
of inaccessible points located on the building structure. Due to the dispersion
of tested points over large object as well as to existing difficulties with visibility
a method has been elaborated that gives access to points via additional optical elements
– flat mirrors and/or rectangular prisms. In order to protect against external
influences the reflecting area of the mirror and back wall of the prism were
Al+SiO2-coated.
Two optical devices for laser measurements have been planned and purchased
for tests. They have been installed in two-hinge brackets to be able to turn laser
beam toward the prism mounted at measured place. Flexible research stand was
mounted and two tests were performed for the distance up to almost 30 m: a 100-
fold and 10-fold with varying distances. Analysis of the results showed that the designed
set of devices allows the cyclic displacement measurement of multiple
points located within 50 m from the instrument with an accuracy not worse
than ±1 mm.
It has been concluded that proposed approach based on distance measurements
can be expanded by angles what should give the opportunity to determine three
components of the displacement of test points. It is planned to focus further works
on the use of the set: robotic total station + mirrors + reflective targets and control
its stability in spatial displacement surveys to inaccessible points located on engineering
structures or buildings.

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